In prior art wireless communication systems, the implementation for performing an activity transfer such as a handoff was as follows. When the cell-site receiver handling a call from a wireless telephone noticed that the received signal strength from the wireless telephone fell below a predetermined threshold value, the cell site asked a system controller controlling the overall wireless system to determine if a neighboring cell site was receiving the wireless telephone's signal at an adequate signal strength. The system controller in response to the current cell site inquiry sent messages to the neighboring cell sites with a handoff request. Each neighboring cell site scanned for the signal from the wireless telephone on the channel specified by the system controller. When one of the neighboring cell sites reported an adequate signal level to the system controller, the system controller implemented the handoff. This method of determining neighboring cell-sites performs well for conventional cellular systems in which the number of cell sites is reasonably small, and each cell site covers a large geographical region. Because each cell site covers a large geographical region, the number of handoffs that occur is reasonably low.
Whereas this technique of performing handoff has worked well for large cellular telephone systems, in large personal communication systems (PCS), the technique has not been as effective in all situations. The reason is that within a large PCS system, there are potentially hundreds of cell sites each having an extremely small geographical area. In addition, PCS system uses high transmission frequencies and low transmission power resulting in frequent handoffs. Another problem in certain large PCS systems is that they are in office buildings where there are many obstructions, also the physical destination of the wireless handset's user plays a important role in the handoff process. For example, if the handset is moving down a particular hallway in a given direction, then the handoff should be to the next cell site that can handle that hallway in that direction. Note, because of the power and transmission frequencies or obstructions this desired cell site may not be the closest geographical cell site to the hallway. Because of the need to do frequent handoffs for each individual active wireless telephone and the extremely large number of cell sites, the system controller experiences a large real time processing load from performing handoffs. In addition, the PCS system is distinguished from a cellular telephone system in that a cellular telephone system may have each cell site surrounded by only three other cell sites; whereas, the PCS system normally will have each cell site having seven to 32 possible neighbors that may be candidates for a handoff. Further, because of the large number of cell sites in a PCS system, it is very difficult for a system administrator to hand specify for each cell site what are the possible candidate cell sites for handoffs let alone determine the best candidate cell sites based on user traffic patterns. In addition, PCS systems are characterized by constant addition and removal of cell sites.
It is clear that a problem exists with the present method for doing handoffs in large PCS systems since requiring each of the neighboring cell sites to monitor the wireless handset and report back to the system controller places a large real time processing burden on the system controller.